getting output from a c program - c

Question

I compiled the below program:
#include <stdio.h>
#define MAXLINE 1000 /* maximum input line length */
int getline(char line[], int maxline);
void copy(char to[], char from[]);
/* print the longest input line */
main()
{
int len; /* current line length */
int max; /* maximum length seen so far */
char line[MAXLINE]; /* current input line */
char longest[MAXLINE]; /* longest line saved here */
max = 0;
while ((len = getline(line, MAXLINE)) > 0)
if (len > max) {
max = len;
copy(longest, line);
}
if (max > 0) /* there was a line */
printf("%s", longest);
return 0;
}
/* getline: read a line into s, return length */
int getline(char s[],int lim)
{
int c, i;
for (i=0; i < lim-1 && (c=getchar())!=EOF && c!='\n'; ++i)
s[i] = c;
if (c == '\n') {
s[i] = c;
++i;
}
s[i] = '\0';
return i;
}
/* copy: copy 'from' into 'to'; assume to is big enough */
void copy(char to[], char from[])
{
int i;
i = 0;
while ((to[i] = from[i]) != '\0')
++i;
}
I tried to run it in bash shell:
gcc -o longest-line longest-line.c
./longest-line
And basically it turns into a running process (shows in result of ps aux) and the cursor just blinks. In the code, when the program is run and the getline function is called, it does 1000 iterations and the getchar is called each time to get input from the terminal in order to increment the counter if it's not end of file or newline. However, immediately there is no input in the terminal and when I start adding input and press the enter key:
$ ./longest-line
Hello World
Hello Again
Nothing happens. It's supposed to print the longest line.

Answer 1

The problem is that if you press '\n' from keyboard getline will always return 1 because of this statement
if (c == '\n') {
s[i] = c;
++i;
}
and the line while ((len = getline(line, MAXLINE)) > 0) will always be true.
But if you use a file as standard input it will work fine because of the EOF.
If you want it to work from keyboard input press Ctrl-D or Ctrl-Z to simulate an EOF.

Answer 2

So, on my compiler, I had to fix a few minor issues.
Generally, main should be written as int main() { ... } or int main(int argc, char **argv) { ... }.
getline() conflicts with a builtin function that gets pulled in from the #include <stdio.h>, so I simply renamed yours to getline_custom and also renamed all the usage points.
That being said, with these minor fixes, (which may not be required under your compiler), your program works correctly.
I believe your confusion is that the program won't print the longest line until after you've sent EOF. In bash, you can do this with CTRL+D.
Example:
[12:39pm][wlynch#watermelon /tmp] ./foo
test // Then I hit enter
longest line // Then I hit enter
short line // Then I hit enter
one more // Then I hit ctrl-D
longest line // This is output from the program.
Another Example:
If we use redirection, we can more easily see the difference between the input and output.
[12:42pm][wlynch#watermelon /tmp] printf "longest line\nshort line" | ./foo
longest line
or, using an input file:
[12:53pm][wlynch#watermelon /tmp] cat input.txt
longest line
short line
foo
blah
[12:53pm][wlynch#watermelon /tmp] cat input.txt | ./foo
longest line
On the other hand
If, on the other hand, you'd like the program to print the current longest line after each line of input, then we would need to change the code in this program.
Here's an example of that:
int main() {
int len = 0; /* current line length */
int max = 0; /* maximum length seen so far */
char line[MAXLINE]; /* current input line */
char longest[MAXLINE]; /* longest line saved here */
while ((len = getline(line, MAXLINE)) > 0) {
if (len > max) {
max = len;
copy(longest, line);
}
printf("Current longest line: %s", longest);
}
}